Uranium ore deposits
Encyclopedia
Uranium ore deposits are economically recoverable concentrations of uranium
within the Earth
's crust
. Uranium is one of the more common elements in the Earth's crust, some 40 times more common than silver
and 500 times more common than gold
. It can be found almost everywhere in rock, soil, rivers, and oceans. The challenge is to find those areas where the concentrations are adequate to form an economically viable deposit.
Globally, the distribution of uranium ore deposits is widespread on all continents, with the largest deposits found in Australia
, Kazakhstan
, and Canada
. To date, high-grade deposits are only found in the Athabasca Basin
region of Canada.
Uranium deposits are generally classified based on host rocks, structural setting, and mineralogy of the deposit. The most widely used classification scheme was developed by the International Atomic Energy Agency
(IAEA) and subdivides deposits into 15 categories.
lic weakly radioactive
chemical element
. It has the symbol
U and atomic number
92. The most common isotope
s in natural uranium are 238U
(99.27%) and 235U
(0.72%). All uranium isotopes present in natural uranium are radioactive and fissionable
, and 235U is fissile
(will support a neutron-mediated chain reaction). Uranium, thorium
, and potassium
are the main elements contributing to natural terrestrial radioactivity.
Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70% denser
than lead
, but not as dense as tungsten
, gold
, platinum
, iridium
, or osmium
. It is always found combined with other elements. Along with all elements having atomic weight
s higher than that of iron
, it is only naturally formed in supernova
explosions.
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The primary uranium ore mineral is uraninite
(UO2) or pitchblende (UO3, U2O5), commonly collectively referred to as U3O8 (the most stable form). A range of other uranium minerals can be found in various deposits. These include carnotite
, the davidite
-brannerite-absite type uranium titanates, and the euxenite
-fergusonite
-samarskite
group.
A large variety of secondary uranium minerals are known, many of which are brilliantly coloured and fluorescent. The most common are gummite
, autunite
(with calcium
), saleeite
(magnesium
) and torbernite
(with copper
); and hydrated uranium silicates such as coffinite
, uranophane
(with calcium) and sklodowskite (magnesium).
are host mineralogy, reduction-oxidation potential
, and porosity
.
Uranium is a highly soluble, as well as a radioactive, heavy metal. It can be easily dissolved, transported and precipitated within ground waters by subtle changes in oxidation conditions. Uranium also does not usually form very insoluble mineral species, which is a further factor in the wide variety of geological conditions and places in which uranium mineralization may accumulate.
Uranium is an incompatible element within magma
s, and as such it tends to become accumulated within highly fractionated
and evolved granite
melts, particularly alkaline examples. These melts tend to become highly enriched in uranium, thorium
and potassium
, and may in turn create internal pegmatite
s or hydrothermal systems into which uranium may dissolve.
(IAEA) assigns uranium deposits to 15 main categories of deposit types, according to their geological setting and genesis of mineralization, arranged according to their approximate economic significance.
Unconformity-type uranium deposits host high grades relative to other uranium deposits and include some of the largest and richest deposits known. They occur in close proximity to major unconformities
between relatively quartz
-rich sandstone
s comprising the basal portion of relatively undeformed sedimentary basin
s and deformed metamorphic
basement rock
s. These sedimentary basins are typically of Proterozoic
age, however some Phanerozoic
examples exist.
The two most significant areas for this style of deposit are currently the Athabasca Basin
in Saskatchewan
, Canada
, and the McArthur Basin
in the Northern Territory
, Australia
.
with 232 million pounds (105,000 t) U3O8 at an average grade of 19% and McArthur River with 488 million pounds (221,000 t) U3O8 at an average grade of 24%. These deposits occur below, across and immediately above the unconformity.
in the Alligator Rivers
region of the Northern Territory of Australia (including Jabiluka
, Ranger
, and Nabarlek
) are below the unconformity and are at the low-grade end of the unconformity deposit range but are still high grade compared to most uranium deposit types. There has been very little exploration in Australia to locate deeply concealed deposits lying above the unconformity similar to those in Canada. It is possible that very high grade deposits occur in the sandstones above the unconformity in the Alligator Rivers
/Arnhem Land
area.
Phanerozoic unconformity-related deposits occur in Proterozoic metasediments below an unconformity at the base of overlying Phanerozoic sandstone. These deposits are small and low-grade (Bertholene
and Aveyron
deposits, in France).
or mudstone
units are interbedded in the sedimentary sequence and often occur immediately above and below the mineralised horizon. Uranium is mobile under oxidising conditions and precipitates under reducing conditions, and thus the presence of a reducing environment is essential for the formation of uranium deposits in sandstone.
Primary mineralization consists of pitchblende and coffinite, with weathering
producing secondary mineralization. Sandstone deposits constitute about 18% of world uranium resources. Orebodies of this type are commonly low to medium grade (0.05–0.4% U3O8) and individual orebodies are small to medium in size (ranging up to a maximum of 50,000 t U3O8).
Sandstone hosted uranium deposits are widespread globally and span a broad range of host rock ages. Some of the major provinces and production centers include:
Significant potential remains in most of these centers as well as in Australia
, Mongolia
, South America
, and Africa
.
This model type can be further subdivided into the following sub-types:
Many deposits represent combinations of these types.
flow, but on a small scale the ore zones may cut across sedimentary features of the host sandstone. Deposits of this nature commonly occur within palaeochannels cut in the underlying basement rocks.
Tabular sandstone uranium deposits contains many of the highest grades of the sandstone class, however the average deposit size is very small.
and porous
sandstone
s or conglomerates
. The mechanism for deposit formation is dissolution of uranium from the formation or nearby strata
and the transport of this soluble uranium into the host unit. When the fluids change redox
state, generally in contact with carbon
-rich organic matter, uranium precipitates to form a 'front'.
The Rollfront subtype deposits typically represent the largest of the sandstone-hosted uranium deposits and one of the largest uranium deposit types with an average of 21 million lb (9,500 t) U3O8. Included in this class are the Inkai deposit in Kazakhstan
and the Smith Ranch
deposit in Wyoming
. Probably more significant than their larger size, rollfront deposits have the advantage of being amenable to low cost in-situ leach
recovery.
Typical characteristics:
deposits is similar to that for roll-front deposits, above, except that the source of uranium may be in the watershed leading into a stream, or the bed load of the palaeochannel itself. This uranium is transported through the groundwaters and is deposited either at a reduced boundary, or in ephemeral drainage systems such as those in deserts of Namibia and Australia, it is deposited in calcretised evaporation sites or even in saline lakes as the ground water evaporates.
Some particularly rich uranium deposits are formed in palaeochannels which are filled in the lower parts by lignite
or brown coal
, which acts as a particularly efficient reductive trap for uranium. Sometimes, elements such as scandium
, gold
and silver
may be concentrated within these lignite-hosted uranium deposits.
The Frome Embayment in South Australia
hosts several deposits of this type including Honeymoon, Oban, Beverley
and [Four-Mile] (which is the largest deposit of this class). These deposits are hosted in palaeochannels filled with Cainozoic sediments and sourced their uranium from uranium-rich Palaeo- to Mesoproterozoic rocks of the Mount Painter Inlier and the Olary Domain of the Curnamona Province.
in Ontario
, Canada and in the Witwatersrand Supergroup of South Africa
. These deposits make up approximately 13% of the world's uranium resources.
Two main sub-types have been identified:
Quartz pebble conglomerate hosted uranium deposits formed from the transport and deposition of uraninite in a fluvial sedimentary environment and are defined as stratiform and stratabound paleoplacer
deposits. Host rocks are typically submature to supermature, polymictic conglomerates and sandstones deposited in alluvial fan
and braided stream environments. The host conglomerates of the Huronian deposits in Canada are situated at the base of the sequence, whereas the mineralized horizons in the Witwatersand are arguably along tectonized intraformational unconformities.
Uranium minerals were derived from uraniferous pegmatites in the sediment source areas. These deposits are restricted to the Archean
and early Paleoproterozoic
and do not occur in sediments younger than about 2200 million years when oxygen levels in the atmosphere
reached a critical level, making simple uranium oxides no longer stable in near-surface environments.
Quartz pebble conglomerate uranium deposits are typically low grade but characterized by high tonnages. The Huronian deposits in Canada generally contain higher grades (0.15% U3O8) and greater resources (as shown by the Denison
and Quirke
mines), however some of the South African gold deposits also contain sizeable low grade (0.01% U3O8) uranium resources.
.
Uranium minerals in the Witwatersrand deposits are typically uraninite with lesser uranothorite, brannerite, and coffinite. The uranium is especially concentrated along thin carbonaceous seams or carbon leaders. Strong regional scale alteration consists of pyrophyllite
, chloritoid
, muscovite
, chlorite
, quartz, rutile
, and pyrite
. The main elements associated with the uranium are gold and silver. Gold contents are much higher than in the Elliot Lake type with U:Au ranging between 5:1 and 500:1, which indicates that these gold-rich ores are essentially very low grade uranium deposits with gold.
to titanium
-rich with decreasing pebble size and increasing distance from their source. While evidence of post-diagenetic remobilization has been identified, these effects appear far subordinate to the sedimentological controls.
Ore consists of uraninite with lesser brannerite and thucholite. These occur in thin beds exhibiting graded bedding
reminiscent of placer sorting. Alteration is nonexistent to very weak at best and the weak chlorite and sericite
are believed to be mainly post-ore effects. Other post-depositional alteration includes pyritization, silicification, and alteration of titanium minerals. The most prominent geochemical associations with the uranium are thorium and titanium.
It should be noted that this schematic model represents the original depositional setting. The Huronian underwent mild post-depositional folding during the Penokean orogeny
around 1.9 billion years. The main regional structure is the Quirke syncline
along the margins of which the majority of the known deposits are situated. Due to this structural overprint ore bodies range from subhorizontal to steeply dipping
.
Only one iron-ore-copper-gold (IOCG)
deposit of this type is known to contain economically significant quantities of uranium. Olympic Dam
in South Australia
is the world's largest resource of low-grade uranium and accounts for about 66% of Australia's reserves plus resources.
Uranium occurs with copper, gold, silver, and rare earth elements (REE) in a large hematite
-rich granite
breccia
complex in the Gawler Craton
overlain by approximately 300 metres of flat-lying sedimentary rocks of the Stuart Shelf geological province.
Another example for the Breccia type is the Mount Gee area in the Mount Painter Inlier, South Australia. Uranium mineralised quartz-hematite breccia is related to Palaeoproterozoic granites with uranium contents of up to 100 ppm. Hydrothermal processes at about 300 million years ago remobilised uranium from these granites and enriched them in the quartz-hematite breccias. The breccias in the area host a low grade resource of about 31,400 t U3O8 at 615 ppm in average.
Vein
deposits play a special role in the history of uranium: the term "pitchblende" ("Pechblende") originates from German vein deposits when they were mined for silver in the 16th century. F.E. Brückmann made the first mineralogical description of the mineral in 1727 and the vein deposit Jachymov in the Czech Republic
became the type locality for uraninite. In 1789 the German chemist M. H. Klaproth discovered the element of uranium in a sample of pitchblende from the Johanngeorgenstadt vein deposit. The first industrial production of uranium was made from the Jachymov deposit and Marie
and Pierre Curie
used the tailings of the mine for their discovery of polonium
and radium
.
Vein deposits consist of uranium minerals filling in cavities such as cracks, veins, fractures, breccias, and stockwork
s associated with steeply dipping fault systems. There are three major subtypes of vein style uranium mineralisation:
Intragranitc veins form in the late phase of magmatic activity when hot fluids derived from the magma precipitate uranium on cracks within the newly formed granite. Such mineralisation contributed much to the uranium production of France. Veins hosted by metasedimentary units in the exocontact of granites are the most important sources of uranium mineralisation in central Europe including the world class deposits Schneeberg-Schlema-Alberoda in Germany (96,000 t uranium content) as well as Pribram (50,000 t uranium content) and Jachymov (~10,000 t uranium content) in the Czech Republic. Also they are closely related to the granites, the mineralization is much younger with a time gap between granite formation and mineralisation of 20 million years. The initial uranium mineralisation consists of quartz
, carbonate
, fluorite
and pitchblende. Remobilsation of uranium occurred at later stages producing polymetal veins containing silver
, cobalt
, nickel
, arsenic
and other elements. Large deposits of this type can contain more than 1,000 individual mineralized veins. However, only 5 to 12% of the vein areas carry mineralization and although massive lenses of pitchblende can occur, the overall ore grade is only about 0.1% uranium.
The Bohemian Massif
also contains shear zone hosted uranium deposits with the most important one being Rozna-Olsi in Moravia northwest of Brno
. Rozna is currently the only operating uranium mine in central Europe with a total uranium content of 23,000 t and an average grade of 0.24%. The formation of this mineralisation occurred in several stages. After the Variscan Orogeny
, extension took place and hydrothermal fluids overprinted fine grained materials in shear zones with a sulphide-chlorite alteration. Fluids from the overlying sediments entered the basement mobilising uranium and while uprising on the shear zone, the chlorite-pyrite material caused precipitation of uranium minerals in form of coffinite, pitchblende and U-Zr-silicates. This initial mineralisation event took place at about 277 million to 264 million years. During the Triassic a further mineralisation event took place relocating uranium into quartz-carbonate-uranium veins. Another example of this mineralisation style is the Shinkolobwe deposit in Congo, Africa, containing about 30,000 t of uranium.
, pegmatite
and monzonite
s. Major world deposits include Rossing (Namibia
), Ilimaussaq intrusive complex
(Greenland
) and Palabora
(South Africa
).
deposits can contain low grade concentrations of uranium, up to 0.01–0.015% U3O8, within fluorite
or apatite
. These deposits can have a significant tonnage. Very large phosphorite deposits occur in Florida and Idaho
in the United States
, Morocco
, and some middle eastern countries.
of limestone
by groundwater. Pipes are typically filled with down-dropped coarse fragments of limestone and overlying sediments and can be from 30 to 200 m (98.4 to 656.2 ft) wide and up to 1000 metres (3,280.8 ft) deep.
Primary ore minerals are uraninite
and pitchblende, which occur as cavity fills and coatings on quartz
grains within permeable sandstone breccias within the pipe. Resources within individual pipes can range up to 2500 tonnes U3O8 at an average grade of between 0.3 and 1.0% U3O8.
The best known examples of this deposit type are in Arizona
, USA, where several of these deposits have been mined.
to intermediate volcanic to volcaniclastic rocks and associated caldera
subsidence structures, comagmatic intrusions, ring dykes
and diatreme
s.
Mineralization occurs either as structurally controlled veins and breccias discordant to the stratigraphy and less commonly as stratabound mineralization either in extrusive rocks or permeable sedimentary facies. Mineralization may be primary, that is magmatic-related or as secondary mineralization due to leaching, remobilization and re-precipitation. The principal uranium mineral in volcanic deposits is pitchblende, which is usually associated with molybdenite
and minor amounts of lead
, tin
and tungsten
mineralization.
Volcanic hosted uranium deposits occur in host rocks spanning the Precambrian to the Cenozoic but because of the shallow levels at which they form, preservation favors younger age deposits. Some of the more important deposits or districts are Streltsovskoye, Russia; Dornod, Mongolia; and McDermitt, Nevada.
The average deposit size is rather small with grades of 0.02% to 0.2% U3O8. These deposits make up only a small proportion of the world's uranium resources. The only volcanic hosted deposits currently being exploited are those of the Streltsovkoye district of eastern Siberia
. This is in fact not a single stand alone deposit but some 18 individual deposits occurring within the Streltsovsk caldera complex. Nevertheless, the average size of these deposits is far greater than the average volcanic type.
to Recent near-surface uranium concentrations in sediments or soils. Mineralization in calcrete (calcium
and magnesium carbonate
s) are the largest of the surficial deposits. They are interbedded with Tertiary sand and clay, which are usually cemented by calcium and magnesium carbonates. Surficial deposits also occur in peat bogs, karst
caverns and soils.
Surficial deposts account for approximately 4% of world uranium resources. The Yeelirrie deposit is by far the world's largest surficial deposit, averaging 0.15% U3O8. Langer Heinrich in Namibia
is another significant surficial deposit.
metasomatism
. Ore minerals are thorium-rich uraninite
, uranothorite, thorite
, and brannerite. Metasomite are typically small in size and generally contain less than 1000 t U3O8.
Two subtypes are defined based on host lithologies:
Metamorphic deposits those that occur in metasediments or metavolcanic rocks where there is no direct evidence for mineralization post-dating metamorphism. These deposits were formed during regional metamorphism of uranium bearing or mineralized sediments or volcanic pre-cursors.
The most prominent deposits of this type are Mary Kathleen, Queensland
, Australia, and Forstau
, Austria.
deposits (soft brown coal) can contain significant uranium mineralization. Mineralization can also be found in clay and sandstone immediately adjacent to lignite deposits. Uranium has been adsorbed onto carbonaceous matter and as a result no discrete uranium minerals have formed. Deposits of this type are known from the Serres Basin, in Greece
, and in North and South Dakota
in the USA. The uranium content in these deposits is very low, on average less than 0.005% U3O8, and does not currently warrant commercial extraction.
containing 254,000 t of uranium. However, there are estimates for black shales in the USA and Brasil assuming a uranium content of over 1 million tonnes, but at grades below 100 ppm uranium. The Chattanooga Shale in the southeastern USA for example is estimated to contain 4 to 5 million tonnes at an average grade of 54 ppm.
Because of their low grades, no black shale deposit ever produced significant amounts of uranium with one exception: the Ronneburg deposit in eastern Thuringia, Germany. The Ordovician and Silurian black shales at Ronneburg have a background uranium content of 40 to 60 ppm. However, hydrothermal and supergene
processes caused remobilsation and enrichment of the uranium. The production between 1950 and 1990 was about 100,000 t of uranium at average grades of 700 to 1,000 ppm. Measured and inferred resources containg 87,000 t uranium at grades between 200 and 900 ppm are left.
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
within the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
. Uranium is one of the more common elements in the Earth's crust, some 40 times more common than silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
and 500 times more common than gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
. It can be found almost everywhere in rock, soil, rivers, and oceans. The challenge is to find those areas where the concentrations are adequate to form an economically viable deposit.
Globally, the distribution of uranium ore deposits is widespread on all continents, with the largest deposits found in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
, and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. To date, high-grade deposits are only found in the Athabasca Basin
Athabasca Basin
This article is about the uranium mining region near Lake Athabasca. Not to be confused with the drainage basin of the Athabasca River.The Athabasca Basin is a region of Northern Saskatchewan and Alberta Canada that is best known as the world's leading source of high grade uranium...
region of Canada.
Uranium deposits are generally classified based on host rocks, structural setting, and mineralogy of the deposit. The most widely used classification scheme was developed by the International Atomic Energy Agency
International Atomic Energy Agency
The International Atomic Energy Agency is an international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons. The IAEA was established as an autonomous organization on 29 July 1957...
(IAEA) and subdivides deposits into 15 categories.
Uranium
Uranium is a silvery-gray metalMetal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
lic weakly radioactive
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
. It has the symbol
Chemical symbol
A chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element, usually derived from the name of the element, often in Latin. Only the first letter is capitalised...
U and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
92. The most common isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s in natural uranium are 238U
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
(99.27%) and 235U
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...
(0.72%). All uranium isotopes present in natural uranium are radioactive and fissionable
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...
, and 235U is fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...
(will support a neutron-mediated chain reaction). Uranium, thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
, and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
are the main elements contributing to natural terrestrial radioactivity.
Uranium has the highest atomic weight of the naturally occurring elements and is approximately 70% denser
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
than lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, but not as dense as tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
, platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
, iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
, or osmium
Osmium
Osmium is a chemical element with the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-blacktransition metal in the platinum family, and is the densest natural element. Osmium is twice as dense as lead. The density of osmium is , slightly greater than that of iridium,...
. It is always found combined with other elements. Along with all elements having atomic weight
Atomic weight
Atomic weight is a dimensionless physical quantity, the ratio of the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12...
s higher than that of iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, it is only naturally formed in supernova
Supernova
A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
explosions.
Uranium minerals
Uraninite
Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements...
(UO2) or pitchblende (UO3, U2O5), commonly collectively referred to as U3O8 (the most stable form). A range of other uranium minerals can be found in various deposits. These include carnotite
Carnotite
Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K222·3H2O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present.-Occurrence:...
, the davidite
Davidite
Davidite is a rare earth oxide mineral with chemical end members La and Ce. It exists in two forms:*Davidite- 20O38 discovered at Radium Hill mine, South Australia in 1906 and named for Australian geologist Tenatt William Edgeworth David .*Davidite- 20O38 first described in 1960 from Vemork,...
-brannerite-absite type uranium titanates, and the euxenite
Euxenite
Euxenite or euxenite- is a brownish black mineral with a metallic luster.-Chemistry:It contains calcium, niobium, tantalum, cerium, titanium, yttrium, and typically uranium and thorium, with some other metals. The chemical formula is: 2O6...
-fergusonite
Fergusonite
Fergusonite is a mineral comprising a complex oxide of various rare earth elements. The chemical formula of fergusonite species is NbO4, where RE = rare-earth elements in solid solution with Y. Yttrium is usually dominant , but sometimes Ce or Nd may predominate in molar proportion...
-samarskite
Samarskite
Samarskite is a radioactive rare earth mineral series which includessamarskite- with formula: 22O8and samarskite- with formula 22O8 The formula for smarskite- is also given as: O4...
group.
A large variety of secondary uranium minerals are known, many of which are brilliantly coloured and fluorescent. The most common are gummite
Gummite
Gummite is a yellow amorphous mixture of uranium minerals, oxides, silicates and hydrates of uranium, derived from the alteration of uraninite. It is named for its gum-like consistence....
, autunite
Autunite
Autunite with formula: Ca22·10-12H2O is a yellow - greenish fluorescent mineral with a hardness of 2 - 2½. Autunite crystallizes in the tetragonal system and often occurs as tabular square crystals. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore...
(with calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
), saleeite
Saleeite
Saleeite is a secondary uranium mineral occurring in the oxidized zones of uranium deposits, or as disseminations in carnotite-bearing sandstones...
(magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
) and torbernite
Torbernite
The chemical formula of torbenite is similar to that of autunite in which a Cu2+ cation replaces a Ca2+. The number of water hydration molecules can vary between 12 and 8, giving rise to the variety of metatorbernite when torbernite spontaneously dehydrates...
(with copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
); and hydrated uranium silicates such as coffinite
Coffinite
Coffinite is a uranium-bearing silicate mineral with formula: U1-x4x.It occurs as black incrustations, dark to pale-brown in thin section. It has a grayish black streak. It has a brittle to conchoidal fracture. The hardness of coffinite is between 5 and 6.It was first described in 1954 for an...
, uranophane
Uranophane
Uranophane Ca22·5H2O is a rare calcium uranium silicate hydrate mineral that forms from the oxidation of uranium bearing minerals. Uranophane is also known as uranotile. It has a yellow color and is radioactive....
(with calcium) and sklodowskite (magnesium).
| Uranium Minerals | |
|---|---|
| Primary uranium minerals | |
| Name | Chemical Formula |
| uraninite Uraninite Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements... |
UO2 |
| pitchblende | U3O8, rare U3O7 |
| coffinite Coffinite Coffinite is a uranium-bearing silicate mineral with formula: U1-x4x.It occurs as black incrustations, dark to pale-brown in thin section. It has a grayish black streak. It has a brittle to conchoidal fracture. The hardness of coffinite is between 5 and 6.It was first described in 1954 for an... |
U(SiO4)1–x(OH)4x |
| brannerite | UTi2O6 |
| davidite Davidite Davidite is a rare earth oxide mineral with chemical end members La and Ce. It exists in two forms:*Davidite- 20O38 discovered at Radium Hill mine, South Australia in 1906 and named for Australian geologist Tenatt William Edgeworth David .*Davidite- 20O38 first described in 1960 from Vemork,... |
(REE)(Y,U)(Ti,Fe3+)20O38 |
| thucholite | Uranium-bearing pyrobitumen |
| Secondary uranium minerals | |
| Name | Chemical Formula |
| autunite Autunite Autunite with formula: Ca22·10-12H2O is a yellow - greenish fluorescent mineral with a hardness of 2 - 2½. Autunite crystallizes in the tetragonal system and often occurs as tabular square crystals. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore... |
Ca(UO2)2(PO4)2 x 8-12 H2O |
| carnotite Carnotite Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula: K222·3H2O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present.-Occurrence:... |
K2(UO2)2(VO4)2 x 1–3 H2O |
| gummite Gummite Gummite is a yellow amorphous mixture of uranium minerals, oxides, silicates and hydrates of uranium, derived from the alteration of uraninite. It is named for its gum-like consistence.... |
gum like amorphous mixture of various uranium minerals |
| seleeite | Mg(UO2)2(PO4)2 x 10 H2O |
| torbernite Torbernite The chemical formula of torbenite is similar to that of autunite in which a Cu2+ cation replaces a Ca2+. The number of water hydration molecules can vary between 12 and 8, giving rise to the variety of metatorbernite when torbernite spontaneously dehydrates... |
Cu(UO2)2(PO4)2 x 12 H2O |
| tyuyamunite | Ca(UO2)2(VO4)2 x 5-8 H2O |
| uranocircite | Ba(UO2)2(PO4)2 x 8-10 H2O |
| uranophane Uranophane Uranophane Ca22·5H2O is a rare calcium uranium silicate hydrate mineral that forms from the oxidation of uranium bearing minerals. Uranophane is also known as uranotile. It has a yellow color and is radioactive.... |
Ca(UO2)2(HSiO4)2 x 5 H2O |
| zeunerite Zeunerite Zeunerite is a green copper uranium arsenate mineral with formula Cu22•10-16. It is a member of the autunite group. Metazeunerite is a dehydration product.... |
Cu(UO2)2(AsO4)2 x 8-10 H2O |
Ore genesis
There are several themes of uranium ore deposit formation, which are caused by geological and chemical features of rocks and the element uranium. The basic themes of uranium ore genesisOre genesis
The various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
are host mineralogy, reduction-oxidation potential
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
, and porosity
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
.
Uranium is a highly soluble, as well as a radioactive, heavy metal. It can be easily dissolved, transported and precipitated within ground waters by subtle changes in oxidation conditions. Uranium also does not usually form very insoluble mineral species, which is a further factor in the wide variety of geological conditions and places in which uranium mineralization may accumulate.
Uranium is an incompatible element within magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
s, and as such it tends to become accumulated within highly fractionated
Fractional crystallization (geology)
Fractional crystallization is one of the most important geochemical and physical processes operating within the Earth's crust and mantle. Fractional crystallization is the removal and segregation from a melt of mineral precipitates; except in special cases, removal of the crystals changes the...
and evolved granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
melts, particularly alkaline examples. These melts tend to become highly enriched in uranium, thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
and potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, and may in turn create internal pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
s or hydrothermal systems into which uranium may dissolve.
IAEA Classification (1996)
The International Atomic Energy AgencyInternational Atomic Energy Agency
The International Atomic Energy Agency is an international organization that seeks to promote the peaceful use of nuclear energy, and to inhibit its use for any military purpose, including nuclear weapons. The IAEA was established as an autonomous organization on 29 July 1957...
(IAEA) assigns uranium deposits to 15 main categories of deposit types, according to their geological setting and genesis of mineralization, arranged according to their approximate economic significance.
- Unconformity-related deposits
- Sandstone deposits
- Quartz-pebble conglomerate deposits
- Breccia complex deposits
- Vein deposits
- Intrusive deposits (Alaskites)
- Phosphorite deposits
- Collapse breccia pipe deposits
- Volcanic deposits
- Surficial deposits
- Metasomatite deposits
- Metamorphic deposits
- Lignite
- Black shale deposits
- Other types of deposits
Alternate scheme
The IAEA classification scheme works well, but is far from ideal, as it does not consider that similar processes may form many deposit types, yet in a different geological setting. The following table groups the above deposit types based on their environment of deposition.| Uranium Deposit Classification | |
|---|---|
| Uranium Transport / Precipitation Conditions |
Deposit Type |
| Surface Processes / synsedimentary | Surficial deposits |
| Quartz-pebble conglomerate deposits | |
| Phosphorite deposits | |
| Lignite | |
| Black shales | |
| Diagenetic | Sandstone deposits |
| Diagenetic – Hydrothermal? | Unconformity-related deposits |
| Vein deposits | |
| Collapse breccia pipe deposits | |
| Magmatic – Hydrothermal? | Breccia complex deposits |
| Volcanic deposits | |
| Metasomatite deposits | |
| Vein deposits | |
| Intrusive deposits | |
| Metamorphic – Hydrothermal? | Metamorphic deposits |
Unconformity-related deposits
Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe...
between relatively quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
-rich sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s comprising the basal portion of relatively undeformed sedimentary basin
Sedimentary basin
The term sedimentary basin is used to refer to any geographical feature exhibiting subsidence and consequent infilling by sedimentation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification...
s and deformed metamorphic
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
basement rock
Basement Rock
Basement or Basement Rock music was a sub-genre coined in 2006 in an article by music magazine TGR. This was first in relation to the existence of underground record label Criminal Records but more for the independent bands they represent. The roots of the sub-genre are noted to be as far back as...
s. These sedimentary basins are typically of Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
age, however some Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
examples exist.
The two most significant areas for this style of deposit are currently the Athabasca Basin
Athabasca Basin
This article is about the uranium mining region near Lake Athabasca. Not to be confused with the drainage basin of the Athabasca River.The Athabasca Basin is a region of Northern Saskatchewan and Alberta Canada that is best known as the world's leading source of high grade uranium...
in Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, and the McArthur Basin
McArthur Basin
The McArthur Basin is a large intracratonic sedimentary basin in northern Australia, with an exposed area of about 180,000 km2. Most of it lies within the northeastern Northern Territory, but extends over the border into the state of Queensland...
in the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Canada: McArthur River deposits (Athabasca Basin)
The highest grade uranium deposits are found in the Athabasca Basin in Canada, including the two largest high grade uranium deposits in the world, Cigar LakeCigar Lake Mine
The Cigar Lake Mine is the largest undeveloped high grade uranium deposit in the world, located in the uranium rich Athabasca Basin of northern Saskatchewan, Canada....
with 232 million pounds (105,000 t) U3O8 at an average grade of 19% and McArthur River with 488 million pounds (221,000 t) U3O8 at an average grade of 24%. These deposits occur below, across and immediately above the unconformity.
Australia: Alligator Rivers deposits (McArthur Basin)
The deposits of the McArthur River basinMcArthur Basin
The McArthur Basin is a large intracratonic sedimentary basin in northern Australia, with an exposed area of about 180,000 km2. Most of it lies within the northeastern Northern Territory, but extends over the border into the state of Queensland...
in the Alligator Rivers
Alligator Rivers
The Alligator Rivers is the name of a region in the Arnhem Land region of the Northern Territory of Australia, containing three rivers the East, West and South Alligator River...
region of the Northern Territory of Australia (including Jabiluka
Jabiluka
Jabiluka is a uranium deposit and mine development in the Northern Territory of Australia that was to have been built on land belonging to the Mirarr Aboriginal people...
, Ranger
Ranger Uranium Mine
The Ranger uranium mine is surrounded by Kakadu National Park, in the Northern Territory of Australia, 230 km east of Darwin. The orebody was discovered in 1969, and the mine commenced operation in 1980, reaching full production of uranium oxide in 1981...
, and Nabarlek
Nabarlek Uranium Mine
The Nabarlek Mine is a past producing uranium mine in the Northern Territory of Australia. The deposit sits within the Alligator Rivers Uranium Field approximately northeast of Jabiru. It was discovered by Queensland Mines Limited in 1970 by following up an intense airborne radiometric...
) are below the unconformity and are at the low-grade end of the unconformity deposit range but are still high grade compared to most uranium deposit types. There has been very little exploration in Australia to locate deeply concealed deposits lying above the unconformity similar to those in Canada. It is possible that very high grade deposits occur in the sandstones above the unconformity in the Alligator Rivers
Alligator Rivers
The Alligator Rivers is the name of a region in the Arnhem Land region of the Northern Territory of Australia, containing three rivers the East, West and South Alligator River...
/Arnhem Land
Arnhem Land
The Arnhem Land Region is one of the five regions of the Northern Territory of Australia. It is located in the north-eastern corner of the territory and is around 500 km from the territory capital Darwin. The region has an area of 97,000 km² which also covers the area of Kakadu National...
area.
Phanerozoic unconformity-related deposits occur in Proterozoic metasediments below an unconformity at the base of overlying Phanerozoic sandstone. These deposits are small and low-grade (Bertholene
Bertholène
Bertholène is a commune in the Aveyron department in southern France.-Population:-References:*...
and Aveyron
Aveyron
Aveyron is a département in southern France named after the Aveyron River.- History :Aveyron is one of the original 83 departments created during the French Revolution on 4 March 1790....
deposits, in France).
Sandstone deposits
Sandstone deposits are contained within medium to coarse-grained sandstones deposited in a continental fluvial or marginal marine sedimentary environment. Impermeable shaleShale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
or mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
units are interbedded in the sedimentary sequence and often occur immediately above and below the mineralised horizon. Uranium is mobile under oxidising conditions and precipitates under reducing conditions, and thus the presence of a reducing environment is essential for the formation of uranium deposits in sandstone.
Primary mineralization consists of pitchblende and coffinite, with weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
producing secondary mineralization. Sandstone deposits constitute about 18% of world uranium resources. Orebodies of this type are commonly low to medium grade (0.05–0.4% U3O8) and individual orebodies are small to medium in size (ranging up to a maximum of 50,000 t U3O8).
Sandstone hosted uranium deposits are widespread globally and span a broad range of host rock ages. Some of the major provinces and production centers include:
- the WyomingUranium mining in WyomingUranium mining in Wyoming, a state of the United States was formerly a much larger industry than it is today. Wyoming once had many operating uranium mines, and still has the largest known uranium ore reserves of any state in the U.S. The Wyoming uranium mining industry was hard-hit in the 1980s...
basins - the Grants District of New MexicoNew MexicoNew Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
- deposits in Central EuropeCentral EuropeCentral Europe or alternatively Middle Europe is a region of the European continent lying between the variously defined areas of Eastern and Western Europe...
and - KazakhstanKazakhstanKazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
Significant potential remains in most of these centers as well as in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
.
This model type can be further subdivided into the following sub-types:
- tabular
- roll front
- basal channel
- structurally related
Many deposits represent combinations of these types.
Tabular
Tabular deposits consist of irregular tabular or elongate lenticular zones of uranium mineralisation within selectively reduced sediments. The mineralised zones are oriented parallel to the direction of groundwaterGroundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
flow, but on a small scale the ore zones may cut across sedimentary features of the host sandstone. Deposits of this nature commonly occur within palaeochannels cut in the underlying basement rocks.
Tabular sandstone uranium deposits contains many of the highest grades of the sandstone class, however the average deposit size is very small.
Roll front
Roll-front uranium deposits are generally hosted within permeablePermeability (fluid)
Permeability in fluid mechanics and the earth sciences is a measure of the ability of a porous material to allow fluids to pass through it.- Units :...
and porous
Porosity
Porosity or void fraction is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s or conglomerates
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
. The mechanism for deposit formation is dissolution of uranium from the formation or nearby strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
and the transport of this soluble uranium into the host unit. When the fluids change redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
state, generally in contact with carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
-rich organic matter, uranium precipitates to form a 'front'.
The Rollfront subtype deposits typically represent the largest of the sandstone-hosted uranium deposits and one of the largest uranium deposit types with an average of 21 million lb (9,500 t) U3O8. Included in this class are the Inkai deposit in Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
and the Smith Ranch
Smith Ranch-Highland
Smith Ranch and Highland are uranium mining operations located in Wyoming, U.S.A. They are separate permits, operated as a single operation, and have one central processing facility. The Smith Ranch-Highland operation is the largest uranium production facility in the United States.Smith Ranch and...
deposit in Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
. Probably more significant than their larger size, rollfront deposits have the advantage of being amenable to low cost in-situ leach
In-situ leach
In-situ leaching , also called in-situ recovery or solution mining, is a mining process used to recover minerals such as copper and uranium through boreholes drilled into a deposit, in situ....
recovery.
Typical characteristics:
- roll-front deposits are crescent-shaped bodies that transect the host lithologyLithologyThe lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...
- typically the convex side points down the hydraulic gradient.
- the limbs or tails tend to be peneconcordant with the lithology.
- most ore-bodies consist of several interconnected rolls.
- individual roll-front deposits are quite small but collectively can extend for considerable distances.
Basal channel (palaeochannel)
Basal channel deposits are often grouped with tabular or rollfront deposits, depending on their unique characteristics. The model for formation of palaeochannelPalaeochannel
Palaeochannels or paleochannels are deposits of unconsolidated sediments or semi-consolidated sedimentary rocks deposited in ancient, currently inactive river and stream channel systems. The word palaeochannel is formed from the words "palaeo" or 'old', and channel; ie; a palaeochannel is an old...
deposits is similar to that for roll-front deposits, above, except that the source of uranium may be in the watershed leading into a stream, or the bed load of the palaeochannel itself. This uranium is transported through the groundwaters and is deposited either at a reduced boundary, or in ephemeral drainage systems such as those in deserts of Namibia and Australia, it is deposited in calcretised evaporation sites or even in saline lakes as the ground water evaporates.
Some particularly rich uranium deposits are formed in palaeochannels which are filled in the lower parts by lignite
Lignite
Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...
or brown coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
, which acts as a particularly efficient reductive trap for uranium. Sometimes, elements such as scandium
Scandium
Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic transition metal, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids...
, gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
and silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
may be concentrated within these lignite-hosted uranium deposits.
The Frome Embayment in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
hosts several deposits of this type including Honeymoon, Oban, Beverley
Beverley Uranium Mine
The Beverley Mine is Australia's third uranium mine and Australia's first operating in-situ recovery mine. It is located 35 km from Lake Frome at the northern end of the Flinders Ranges in South Australia and opened in 2001...
and [Four-Mile] (which is the largest deposit of this class). These deposits are hosted in palaeochannels filled with Cainozoic sediments and sourced their uranium from uranium-rich Palaeo- to Mesoproterozoic rocks of the Mount Painter Inlier and the Olary Domain of the Curnamona Province.
Structurally related
Tectonic-lithologic controlled uranium deposits occur in sandstones adjacent to a permeable fault zone which cuts the sandstone/mudstone sequence. Mineralisation forms tongue-shaped ore zones along the permeable sandstone layers adjacent to the fault. Often there are a number of mineralised zones 'stacked' vertically on top of each other within sandstone units adjacent to the fault zone.Quartz-pebble conglomerate deposits
Quartz pebble conglomerate hosted uranium deposits are of historical significance as the major source of primary production for several decades after World War 2. This type of deposit has been identified in eight localities around the world, however the most significant deposits are in the Huronian SupergroupHuronian Supergroup
The Huronian Supergroup is a Proterozoic geologic feature of the Superior craton of the Canadian Shield in Ontario and Quebec. It extends from the city of Sault Ste. Marie in the west to the Ontario-Quebec border to the east....
in Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, Canada and in the Witwatersrand Supergroup of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. These deposits make up approximately 13% of the world's uranium resources.
Two main sub-types have been identified:
- Elliot Lake
- WitwatersrandWitwatersrandThe Witwatersrand is a low, sedimentary range of hills, at an elevation of 1700–1800 metres above sea-level, which runs in an east-west direction through Gauteng in South Africa. The word in Afrikaans means "the ridge of white waters". Geologically it is complex, but the principal formations...
Quartz pebble conglomerate hosted uranium deposits formed from the transport and deposition of uraninite in a fluvial sedimentary environment and are defined as stratiform and stratabound paleoplacer
Placer deposit
In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early...
deposits. Host rocks are typically submature to supermature, polymictic conglomerates and sandstones deposited in alluvial fan
Alluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...
and braided stream environments. The host conglomerates of the Huronian deposits in Canada are situated at the base of the sequence, whereas the mineralized horizons in the Witwatersand are arguably along tectonized intraformational unconformities.
Uranium minerals were derived from uraniferous pegmatites in the sediment source areas. These deposits are restricted to the Archean
Archean
The Archean , also spelled Archeozoic or Archæozoic) is a geologic eon before the Paleoproterozoic Era of the Proterozoic Eon, before 2.5 Ga ago. Instead of being based on stratigraphy, this date is defined chronometrically...
and early Paleoproterozoic
Paleoproterozoic
The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
and do not occur in sediments younger than about 2200 million years when oxygen levels in the atmosphere
Great Oxygenation Event
The Great Oxygenation Event , also called the Oxygen Catastrophe or Oxygen Crisis or Great Oxidation, was the biologically induced appearance of free oxygen in Earth's atmosphere. This major environmental change happened around 2.4 billion years ago.Photosynthesis was producing oxygen both before...
reached a critical level, making simple uranium oxides no longer stable in near-surface environments.
Quartz pebble conglomerate uranium deposits are typically low grade but characterized by high tonnages. The Huronian deposits in Canada generally contain higher grades (0.15% U3O8) and greater resources (as shown by the Denison
Denison Mine
The Denison Mine is an abandoned uranium mine located approximately 12.5 km north of Elliot Lake, Ontario, owned by Denison Mines Ltd.. The site has been rehabilitated and its tailings facility is currently undergoing environmental monitoring by Denison Environmental Services.The site was the...
and Quirke
Quirke Mine
The Quirke Mine is an abandoned uranium mine located approximately 13.5 km north of Elliot Lake, Ontario, owned and operated by Rio Algom Ltd...
mines), however some of the South African gold deposits also contain sizeable low grade (0.01% U3O8) uranium resources.
Witwatersrand sub-type
In the Witwatersrand deposits ores are found along unconformities, shale and siltstone beds, and carbonaceous seams. The West Rand Group of sediments tend to host the most uranium within the Witwatersrand Supergroup. The uranium rich Dominion Reef is located at the base of the West Rand Supergroup. The Vaal Reef is the most uranium rich reef of the Central Rand Group of sediments. Structural controls on the regional scale are normal faults while on the deposit scale are bedding parallel shears and thrusts. Textural evidence indicates that the uranium and gold have been remobilized to their current sites; however the debate continues if the original deposition was detrital or was entirely hydrothermal, or alternatively related to high grade diagenesisDiagenesis
In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism. These changes happen at relatively low temperatures and pressures...
.
Uranium minerals in the Witwatersrand deposits are typically uraninite with lesser uranothorite, brannerite, and coffinite. The uranium is especially concentrated along thin carbonaceous seams or carbon leaders. Strong regional scale alteration consists of pyrophyllite
Pyrophyllite
Pyrophyllite is a phyllosilicate mineral composed of aluminium silicate hydroxide: Al2Si4O102. It occurs in two more or less distinct varieties, namely, as crystalline folia and as compact masses; distinct crystals are not known....
, chloritoid
Chloritoid
Chloritoid is a silicate mineral of metamorphic origin. It is an iron magnesium manganese alumino-silicate hydroxide with formula: 2Al4Si2O104. It occurs as greenish grey to black platy micaceous crystals and foliated masses. Its Mohs hardness is 6.5, unusually high for a platy mineral, and it has...
, muscovite
Muscovite
Muscovite is a phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a highly-perfect basal cleavage yielding remarkably-thin laminæ which are often highly elastic...
, chlorite
Chlorite group
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn....
, quartz, rutile
Rutile
Rutile is a mineral composed primarily of titanium dioxide, TiO2.Rutile is the most common natural form of TiO2. Two rarer polymorphs of TiO2 are known:...
, and pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...
. The main elements associated with the uranium are gold and silver. Gold contents are much higher than in the Elliot Lake type with U:Au ranging between 5:1 and 500:1, which indicates that these gold-rich ores are essentially very low grade uranium deposits with gold.
Elliot Lake sub-type
Sedimentological controls on the Huronian deposits of the Elliot Lake district appear to be much stronger than in the Witwatersrand deposits. Ores grade from uranium through thoriumThorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
to titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
-rich with decreasing pebble size and increasing distance from their source. While evidence of post-diagenetic remobilization has been identified, these effects appear far subordinate to the sedimentological controls.
Ore consists of uraninite with lesser brannerite and thucholite. These occur in thin beds exhibiting graded bedding
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
reminiscent of placer sorting. Alteration is nonexistent to very weak at best and the weak chlorite and sericite
Sericite
Sericite is a fine grained mica, similar to muscovite, illite, or paragonite. Sericite is a common alteration mineral of orthoclase or plagioclase feldspars in areas that have been subjected to hydrothermal alteration typically associated with copper, tin, or other hydrothermal ore deposits...
are believed to be mainly post-ore effects. Other post-depositional alteration includes pyritization, silicification, and alteration of titanium minerals. The most prominent geochemical associations with the uranium are thorium and titanium.
It should be noted that this schematic model represents the original depositional setting. The Huronian underwent mild post-depositional folding during the Penokean orogeny
Penokean orogeny
The Penokean orogeny was a mountain-building episode that occurred in the early Proterozoic about 1.85 to 1.84 billion years ago, in the area of North America that would eventually become Minnesota, Wisconsin, Michigan and Ontario...
around 1.9 billion years. The main regional structure is the Quirke syncline
Syncline
In structural geology, a syncline is a fold, with younger layers closer to the center of the structure. A synclinorium is a large syncline with superimposed smaller folds. Synclines are typically a downward fold, termed a synformal syncline In structural geology, a syncline is a fold, with younger...
along the margins of which the majority of the known deposits are situated. Due to this structural overprint ore bodies range from subhorizontal to steeply dipping
Strike and dip
Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented...
.
Breccia complex deposits (IOCG-U)
Iron oxide copper gold ore deposits
Iron oxide copper gold ore deposits are important and highly valuable concentrations of copper, gold and uranium ores hosted within iron oxide dominant gangue assemblages which share a common genetic origin....
deposit of this type is known to contain economically significant quantities of uranium. Olympic Dam
Olympic Dam, South Australia
Olympic Dam is a mining centre in South Australia located some 550 km NNW of Adelaide, the capital city of South Australia. It is the site of an extremely large iron oxide copper gold deposit producing copper, uranium, gold and silver. The site hosts an underground mine as well as an...
in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
is the world's largest resource of low-grade uranium and accounts for about 66% of Australia's reserves plus resources.
Uranium occurs with copper, gold, silver, and rare earth elements (REE) in a large hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
-rich granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
complex in the Gawler Craton
Gawler craton
The Gawler Craton covers approximately 440,000 square kilometres of central South Australia. Its Precambrian crystalline basement crustal block was cratonised ca. 1550-1450 Ma...
overlain by approximately 300 metres of flat-lying sedimentary rocks of the Stuart Shelf geological province.
Another example for the Breccia type is the Mount Gee area in the Mount Painter Inlier, South Australia. Uranium mineralised quartz-hematite breccia is related to Palaeoproterozoic granites with uranium contents of up to 100 ppm. Hydrothermal processes at about 300 million years ago remobilised uranium from these granites and enriched them in the quartz-hematite breccias. The breccias in the area host a low grade resource of about 31,400 t U3O8 at 615 ppm in average.
Vein deposits
Vein (geology)
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...
deposits play a special role in the history of uranium: the term "pitchblende" ("Pechblende") originates from German vein deposits when they were mined for silver in the 16th century. F.E. Brückmann made the first mineralogical description of the mineral in 1727 and the vein deposit Jachymov in the Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
became the type locality for uraninite. In 1789 the German chemist M. H. Klaproth discovered the element of uranium in a sample of pitchblende from the Johanngeorgenstadt vein deposit. The first industrial production of uranium was made from the Jachymov deposit and Marie
Marie Curie
Marie Skłodowska-Curie was a physicist and chemist famous for her pioneering research on radioactivity. She was the first person honored with two Nobel Prizes—in physics and chemistry...
and Pierre Curie
Pierre Curie
Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...
used the tailings of the mine for their discovery of polonium
Polonium
Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie Skłodowska-Curie and Pierre Curie. A rare and highly radioactive element, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for...
and radium
Radium
Radium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
.
Vein deposits consist of uranium minerals filling in cavities such as cracks, veins, fractures, breccias, and stockwork
Stockwork
In geology, a stockwork is a complex system of structurally controlled or randomly oriented veins. Stockworks are common in many ore deposit types and especially notable in greisens. They are also referred to as stringer zones....
s associated with steeply dipping fault systems. There are three major subtypes of vein style uranium mineralisation:
- intragranitic veins (Central Massif, France)
- veins in metasedimentary rocks in exocontacts of granites
- quartz-carbonate uranium veins (Erzgebirge Mts, Germany/Czech Republic; Bohemian Massif, Czech Republic)
- uranium-polymetal veins (Erzgebirge Mts, Germany/Czech Republic; Saskatchewan, Canada)
- mineralised fault and shear zones (central Africa; Bohemian Massif, Czech Republic)
Intragranitc veins form in the late phase of magmatic activity when hot fluids derived from the magma precipitate uranium on cracks within the newly formed granite. Such mineralisation contributed much to the uranium production of France. Veins hosted by metasedimentary units in the exocontact of granites are the most important sources of uranium mineralisation in central Europe including the world class deposits Schneeberg-Schlema-Alberoda in Germany (96,000 t uranium content) as well as Pribram (50,000 t uranium content) and Jachymov (~10,000 t uranium content) in the Czech Republic. Also they are closely related to the granites, the mineralization is much younger with a time gap between granite formation and mineralisation of 20 million years. The initial uranium mineralisation consists of quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....
, fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
and pitchblende. Remobilsation of uranium occurred at later stages producing polymetal veins containing silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
, cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
, nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
and other elements. Large deposits of this type can contain more than 1,000 individual mineralized veins. However, only 5 to 12% of the vein areas carry mineralization and although massive lenses of pitchblende can occur, the overall ore grade is only about 0.1% uranium.
The Bohemian Massif
Bohemian Massif
The Bohemian Massif; or Český masiv; is in the geology of Central Europe a large massif stretching over central Czech republic, eastern Germany, southern Poland and northern Austria...
also contains shear zone hosted uranium deposits with the most important one being Rozna-Olsi in Moravia northwest of Brno
Brno
Brno by population and area is the second largest city in the Czech Republic, the largest Moravian city, and the historical capital city of the Margraviate of Moravia. Brno is the administrative centre of the South Moravian Region where it forms a separate district Brno-City District...
. Rozna is currently the only operating uranium mine in central Europe with a total uranium content of 23,000 t and an average grade of 0.24%. The formation of this mineralisation occurred in several stages. After the Variscan Orogeny
Variscan orogeny
The Variscan orogeny is a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica and Gondwana to form the supercontinent of Pangaea.-Naming:...
, extension took place and hydrothermal fluids overprinted fine grained materials in shear zones with a sulphide-chlorite alteration. Fluids from the overlying sediments entered the basement mobilising uranium and while uprising on the shear zone, the chlorite-pyrite material caused precipitation of uranium minerals in form of coffinite, pitchblende and U-Zr-silicates. This initial mineralisation event took place at about 277 million to 264 million years. During the Triassic a further mineralisation event took place relocating uranium into quartz-carbonate-uranium veins. Another example of this mineralisation style is the Shinkolobwe deposit in Congo, Africa, containing about 30,000 t of uranium.
Intrusive associated deposits
Intrusive deposits make up a large proportion of the world's uranium resources. Included in this type are those associated with intrusive rocks including alaskite, graniteGranite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
, pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
and monzonite
Monzonite
Monzonite is an intermediate igneous intrusive rock composed of approximately equal amounts of sodic to intermediate plagioclase and orthoclase feldspars with minor amounts of hornblende, biotite and other minerals...
s. Major world deposits include Rossing (Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
), Ilimaussaq intrusive complex
Ilimaussaq intrusive complex
The Ilimaussaq intrusive complex is a large alkalic layered intrusion located on the southwest coast of Greenland. It is Mesoproterozoic in age. It is the type locality of agpaitic nepheline syenite and hosts a variety of unusual rock types....
(Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
) and Palabora
Palabora
Palabora Mining Company Limited is a publicly-traded mining company headquartered in Phalaborwa, Limpopo province, South Africa. The company operates a single cluster of open-pit and underground mines producing mainly copper as well as byproducts such as anode slimes, nickel sulphate, sulphuric...
(South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
).
Phosphorite deposits
Marine sedimentary phosphoritePhosphorite
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock which contains high amounts of phosphate bearing minerals. The phosphate content of phosphorite is at least 15 to 20% which is a large enrichment over the typical sedimentary rock content of less than 0.2%...
deposits can contain low grade concentrations of uranium, up to 0.01–0.015% U3O8, within fluorite
Fluorite
Fluorite is a halide mineral composed of calcium fluoride, CaF2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon...
or apatite
Apatite
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH−, F−, Cl− or Br− ions, respectively, in the crystal...
. These deposits can have a significant tonnage. Very large phosphorite deposits occur in Florida and Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
, and some middle eastern countries.
Collapse breccia pipe deposits
Collapse breccia pipe deposits occur within vertical, circular solution collapse structures, formed by the dissolutionDissolution (chemistry)
Dissolution is the process by which a solid, liquid or gas forms a solution in a solvent. In solids this can be explained as the breakdown of the crystal lattice into individual ions, atoms or molecules and their transport into the solvent. For liquids and gases, the molecules must be compatible...
of limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
by groundwater. Pipes are typically filled with down-dropped coarse fragments of limestone and overlying sediments and can be from 30 to 200 m (98.4 to 656.2 ft) wide and up to 1000 metres (3,280.8 ft) deep.
Primary ore minerals are uraninite
Uraninite
Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements...
and pitchblende, which occur as cavity fills and coatings on quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
grains within permeable sandstone breccias within the pipe. Resources within individual pipes can range up to 2500 tonnes U3O8 at an average grade of between 0.3 and 1.0% U3O8.
The best known examples of this deposit type are in Arizona
Arizona breccia pipe uranium mineralization
During the late 1970s and through the 1980s, Mohave and Coconino County, Arizona, immediately north and south of the Grand Canyon and west of the Navajo Indian Reservation were explored for Arizona breccia pipe uranium mineralization...
, USA, where several of these deposits have been mined.
Volcanic deposits
Volcanic deposits occur in felsicFelsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
to intermediate volcanic to volcaniclastic rocks and associated caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...
subsidence structures, comagmatic intrusions, ring dykes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
and diatreme
Diatreme
A diatreme is a breccia-filled volcanic pipe that was formed by a gaseous explosion. Diatremes often breach the surface and produce a tuff cone, a filled relatively shallow crater known as a maar, or other volcanic pipes.- Word origin :...
s.
Mineralization occurs either as structurally controlled veins and breccias discordant to the stratigraphy and less commonly as stratabound mineralization either in extrusive rocks or permeable sedimentary facies. Mineralization may be primary, that is magmatic-related or as secondary mineralization due to leaching, remobilization and re-precipitation. The principal uranium mineral in volcanic deposits is pitchblende, which is usually associated with molybdenite
Molybdenite
Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...
and minor amounts of lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
and tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
mineralization.
Volcanic hosted uranium deposits occur in host rocks spanning the Precambrian to the Cenozoic but because of the shallow levels at which they form, preservation favors younger age deposits. Some of the more important deposits or districts are Streltsovskoye, Russia; Dornod, Mongolia; and McDermitt, Nevada.
The average deposit size is rather small with grades of 0.02% to 0.2% U3O8. These deposits make up only a small proportion of the world's uranium resources. The only volcanic hosted deposits currently being exploited are those of the Streltsovkoye district of eastern Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
. This is in fact not a single stand alone deposit but some 18 individual deposits occurring within the Streltsovsk caldera complex. Nevertheless, the average size of these deposits is far greater than the average volcanic type.
Surficial deposits (calcretes)
Surficial deposits are broadly defined as TertiaryTertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
to Recent near-surface uranium concentrations in sediments or soils. Mineralization in calcrete (calcium
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
and magnesium carbonate
Magnesium carbonate
Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. Several hydrated and basic forms of magnesium carbonate also exist as minerals...
s) are the largest of the surficial deposits. They are interbedded with Tertiary sand and clay, which are usually cemented by calcium and magnesium carbonates. Surficial deposits also occur in peat bogs, karst
KARST
Kilometer-square Area Radio Synthesis Telescope is a Chinese telescope project to which FAST is a forerunner. KARST is a set of large spherical reflectors on karst landforms, which are bowlshaped limestone sinkholes named after the Kras region in Slovenia and Northern Italy. It will consist of...
caverns and soils.
Surficial deposts account for approximately 4% of world uranium resources. The Yeelirrie deposit is by far the world's largest surficial deposit, averaging 0.15% U3O8. Langer Heinrich in Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
is another significant surficial deposit.
Metasomatite deposits
Metasomatite deposits consist of disseminated uranium minerals within structurally deformed rocks that have been affected by intense sodiumSodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
metasomatism
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
. Ore minerals are thorium-rich uraninite
Uraninite
Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2, but also contains UO3 and oxides of lead, thorium, and rare earth elements...
, uranothorite, thorite
Thorite
Thorite, SiO4, is a rare nesosilicate of thorium that crystallizes in the tetragonal system and is isomorphous with zircon and hafnon. It is the most common mineral of thorium and is nearly always strongly radioactive. It was named in 1829 to reflect its thorium content...
, and brannerite. Metasomite are typically small in size and generally contain less than 1000 t U3O8.
Two subtypes are defined based on host lithologies:
- metasomatized granite; ex. Ross Adams deposit in AlaskaAlaskaAlaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, USA. - metasomatised metasediment; ex. Zhovti Vody deposit in Kirovogradska oblast, UkraineUkraineUkraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...
and Valhalla deposit in northwestern QueenslandQueenslandQueensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
, AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Metamorphic deposits
The most prominent deposits of this type are Mary Kathleen, Queensland
Mary Kathleen, Queensland
Mary Kathleen was a mining settlement in the northwestern part of Queensland, Australia. It is located in the Selwyn Range between Mount Isa and Cloncurry.Mary Kathleen was first settled during the 1860s.-Uranium mine:...
, Australia, and Forstau
Forstau
Forstau is a municipality in the St. Johann im Pongau district in the state of Salzburg in Austria....
, Austria.
Lignite
LigniteLignite
Lignite, often referred to as brown coal, or Rosebud coal by Northern Pacific Railroad,is a soft brown fuel with characteristics that put it somewhere between coal and peat...
deposits (soft brown coal) can contain significant uranium mineralization. Mineralization can also be found in clay and sandstone immediately adjacent to lignite deposits. Uranium has been adsorbed onto carbonaceous matter and as a result no discrete uranium minerals have formed. Deposits of this type are known from the Serres Basin, in Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
, and in North and South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
in the USA. The uranium content in these deposits is very low, on average less than 0.005% U3O8, and does not currently warrant commercial extraction.
Black shale deposits
Black shale mineralisations are large low-grade resources of uranium. They form in submarine environments under oxygen-free conditions. Organic matter in clay-rich sediments will not be converted to CO2 by biological processes in this environment and it can reduce and immobilise uranium dissolved in seawater. Average uranium grades of black shales are 50 to 250 ppm. The largest explored resource is Ranstad in SwedenSweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
containing 254,000 t of uranium. However, there are estimates for black shales in the USA and Brasil assuming a uranium content of over 1 million tonnes, but at grades below 100 ppm uranium. The Chattanooga Shale in the southeastern USA for example is estimated to contain 4 to 5 million tonnes at an average grade of 54 ppm.
Because of their low grades, no black shale deposit ever produced significant amounts of uranium with one exception: the Ronneburg deposit in eastern Thuringia, Germany. The Ordovician and Silurian black shales at Ronneburg have a background uranium content of 40 to 60 ppm. However, hydrothermal and supergene
Supergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...
processes caused remobilsation and enrichment of the uranium. The production between 1950 and 1990 was about 100,000 t of uranium at average grades of 700 to 1,000 ppm. Measured and inferred resources containg 87,000 t uranium at grades between 200 and 900 ppm are left.
Other types of deposits
- There are also uranium deposits, of other types, in the JurassicJurassicThe Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
Todilto Limestone in the Grants District, New MexicoNew MexicoNew Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, USA.
- The Freital/Dresden-Gittersee deposit in eastern Germany produced about 3.700 t of uranium from PermianPermianThe PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
hard coal and its host rocks. The average ore grade was 0.11%. The deposit formed in a combination of syngenetic and diagenetic processes.
- In some countries like Hungary and China trials are underway to extract uranium from fly ashFly ashFly ash is one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases. Ash which does not rise is termed bottom ash. In an industrial context, fly ash usually refers to ash produced during combustion of coal...
.
See also
- List of countries by uranium reserves
- Ore genesisOre genesisThe various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
- UraniumUraniumUranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
- List of uranium mines
- Uranium miningUranium miningUranium mining is the process of extraction of uranium ore from the ground. The worldwide production of uranium in 2009 amounted to 50,572 tonnes, of which 27% was mined in Kazakhstan. Kazakhstan, Canada, and Australia are the top three producers and together account for 63% of world uranium...
- Uranium depletionUranium depletionUranium depletion is the result of extracting and consuming uranium, a non-renewable resource. The availability of high-grade uranium ore will deplete over time meaning the fuel will become more environmentally and economically expensive to extract....
- Nuclear fuel cycleNuclear fuel cycleThe nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...